1. Field of the Invention
The suggested inventions relate to the intra-vision means and are designed for producing visually sensed images of the internal structure of an object, in particular, of a biological object, with X-rays. The preferential applications include defectoscopy and medical diagnostics.
2. Description of the Prior Art
Various methods and devices of the said intended use are known, where traditional principles of projection roentgenoscopy are embodied. In such methods and devices, the visible image of the object's internal structure, for example, tissues of a biological object, is obtained as a shadow projection. Density of the acquired image in each of its points is determined by the total attenuation of X-rays that passed through the object on their way from the source to the detection means. The latter is either a fluorescent screen or an X-ray film, which should be chemically treated to get the image visualized (see Polytechnical Dictionary. Moscow, “Soviet Encyclopedia”, 1976 [1], p. 425; Physics of image visualization in medicine. Edited by S. Webb. Moscow, “Mir”, 1991 [2], p. 40–41).
In the above mentioned known methods and devices, the image of a real three-dimensional structure is acquired as the said two-dimensional shadow projection, which interpretation requires from the specialist who carries out object analysis, in particular, technical or medical diagnostics, respective experience and qualification and, in a number of cases, is problematic. The reasons for this are low contrast, poor signal to noise ratio, inevitable overlapping of the images of structural elements, impossibility of quantitative comparison between individual local fragments by density. Sharpness and contrast of the acquired image also decrease under the influence of quanta of the secondary Compton scattered radiation, hitting the detection means.
X-ray computer tomography methods and devices permitting to acquire a two-dimensional image of a thin layer of a three-dimensional object are known (V. V. Piklov, N. G. Preobrazhenskiy. Computational tomography and physical experiment. The progress of physical sciences, v. 141, 3rd ed., November 1983, p. 469–498 [3]; see also [2], p. 138–146). Such methods are using multiple irradiation of the object under study from different positions and registration of the radiation that passed through this object by a line of detectors. The obtained tissue density distribution of the object in the cross-section under study (target cross-section) is discrete and achieved through computer-assisted solution of combined equations, the order of which as well as the number of resolution elements correspond to the product of the number of positions, from which irradiation is done, by the number of detectors. Doing irradiation in different cross-sections, one can obtain a three-dimensional image of the object based on a set of two-dimensional by-layer images. Computer tomography means permit in principle to obtain an image of sufficiently high quality, and this image presents the picture of tissues density distribution (in contrast to a picture specific to integral absorption of a substance (for example, biological tissues), located in the path of radiation from the source to this or that element of the observed projection.) But this is achieved through a greater number of positions, from which irradiation is done. In this case, the dose of radiation absorbed by the substance is higher, which is undesirable (and in medical applications, is most frequently inadmissible). Presence of Compton scattered radiation is a nuisance factor in this group of known methods and devices too. Both groups of methods and devices used for medical applications are also characterized by the fact, that tissues and organs, which present no interest in the study but are located in the radiation path (both in front and behind the target area), also suffer from intensive radiation (to a lesser degree in the second group of methods and devices than in the first group of methods and devices because when different positions are selected, different tissues and organs surrounding those that are under study are irradiated).
Higher resolving power in the second group of means, requiring a greater number of irradiations from different positions, is limited, first of all, due to inadmissible growth of the dosage. Technical means for acquiring primary data and further image reconstruction is quite complex due to necessity of using fast computers with special software and high-precision requirements to the mechanical structural elements, which must guarantee correct localization of one and the same resolution elements in the target area during their irradiation from different positions. The latter is caused by the fact that the image reconstruction calculations must use the actual data obtained from different irradiation cycles but referring to one and the same resolution elements.
The second above mentioned group of methods and devices, where discrete data on the density of each of the resolution elements is obtained, is the closest one to what is suggested.